[media] soc-camera: Compile fixes for mx2-camera

mx2-camera got broken during the last merge window. This patch
fixes this and removes some unused variables.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>